The disc shaped substrate herein referred to has precisely defined microfluidic structures comprising channels, sample basins, reaction chambers, hydrophobic passages and/or other valve structures etc., by which unit operations may be integrated to create scaled down laboratory processes. Through a high precision spinning of the disc, hundreds of analysis may be performed in parallel on a microscale. An automated procedure may be obtained in an instrument incorporating facilities for dispensing liquid samples and reagents to the disc, for spinning and stopping the disc in order to control the process and the movement of liquid in the microstructures, for collecting data and for moving the disc between the operational modules of the instrument. The microfluidic structures may be integrally formed in the disc, and preferably the disc is disposable and manufactured by a replication technique from a synthetic material, i.e. through molding, embossing or the like.
As used herein, the terms “microfluidic”, “microstructures” etc. contemplate, that a microchannel structure comprises one or more cavities and/or channels that have a depth and/or a width that is ≦103 μm, preferably ≦102 μm. “Fluidic” in addition means that a liquid transport is taking place in the microchannels. The lower limit for the width/breadth is typically significantly larger than the size of the largest reagents and constituents of aliquots that are to pass through a microchannel. The volumes of microcavities/microchambers are typically ≦1000 nl but may extend into the μl-range such as up to 10 μl or 50 μl. Chambers/cavities directly connected to inlet ports may be considerably larger, e.g. microchambers/microcavities intended for application of sample and/or washing liquids.
The terms “microscale”, “microlab” contemplate, that one or more liquid aliquots introduced into a microchannel structure are in the μl-range or smaller, i.e. ≦1000 μl, or in the nl-range such as ≦1000 nl.
The disc comprises covered microchannel structures that are present in a substrate having an axis of symmetry. Each microchannel structure typically is oriented outwards relative to the axis of symmetry with an inlet port at a shorter radial distance from the symmetry axis than a microcavity in which a certain treatment is going to take place, for instance mixing, separation, a chemical reaction, detection etc. There may also be an outlet port for liquid downstream the reaction microcavity. Each microchannel structure may or may not be oriented in a plane perpendicular to the axis of symmetry. By spinning the disc around its axis of symmetry (axis of rotation), a liquid aliquot placed at an inner position, e.g. the inlet port, will be subjected to a centrifugal force driving the liquid outwards, towards and through the microcavity and/or the outlet port for liquids, if present. Vent ports may also be formed and cooperating with liquid flow restrictions in the microchannel structures for controlling the flow direction of liquid aliquots inwards, towards the axis of rotation, through application of centrifugal forces.
According to the invention other forces may also be used for driving liquid flow in this kind of microchannel structures, for instance electrokinetic forces, capillary forces, inertia force other than centrifugal force, over-pressure, etc. This means, for instance, that it is not imperative that the inlet port is at a shorter radial distance from the symmetry axis, than other functional parts of a microchannel structure.
A rotary drive for spinning the disc to create liquid flow in the microfluidic structures is disclosed in a co-pending application titled “ROTARY DRIVE IN AN INSTRUMENT FOR PROCESSING MICROSCALE LIQUID SAMPLE VOLUMES”, assigned to the same applicant and filed on the same day as the present application.
A revolving spindle is contemplated for spinning the disc, the disc being carried on a rotary member connected to the spindle. The drive means must satisfy strict demands for an accurate positioning of the disc at a halt and during spinning for sample preparation and sample dispensing, e.g., for detecting and data collection, e.g., and for high speed spinning during processing. For a time effective operation, the disc must be secured on the rotary member under considerable acceleration and retardation loads. In the process step, the disc may be hastily accelerated to speeds up to about 25,000, such as up to about 10,000, revolutions per minute, or above, and hastily decelerated to a halt.
In the detection step the disc is scanned by a detecting means having a capacity for detecting a particular compound or activity in at least a part area of a detection cavity, such as a fluorescence detector, e.g. In consideration of the microscale dimensions and microscale volumes involved, a rotation that is free from warp and in parallelism with the detector means is then of crucial importance for a repeatable and reliable collection of data.
In this context it is a technical problem in the detection step to secure the planarity and a warp free rotation of the disc shaped substrate and its microstructures in parallelism with the detector means. Therefore, and also for reducing the accelerated mass, it is desired to avoid mechanical structures that would be subject to wear and which may also caused damage to the disc at the point of engagement.
Another technical problem related to spinning the disc in the microlab environment is the necessity for avoiding contaminants such as minute particles down to molecular size, that might originate from frictional wear of mechanical arresting means for holding the disc on the spindle.
It is still another technical problem to initially generate a sealed communication between the adhering side of the disc and a vacuum source, if the disc is not plane. Any irregularities or deviations from the planar condition will produce a leak that impairs on the operation of the vacuum fixation of the disc, and must be avoided to achieve the necessary planarity and parallelism with the detector means.
A rotary drive using sub-pressure for holding a recording medium to a revolving turntable is known from U.S. Pat. No. 4,493,072, wherein a sub-pressure is distributed through channels arranged in a geometric pattern over the contact surface of the turntable.